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import sys
from types import MappingProxyType, DynamicClassAttribute
# try _collections first to reduce startup cost
from _collections import OrderedDict
except ImportError:
from collections import OrderedDict
__all__ = ['EnumMeta', 'Enum', 'IntEnum', 'unique']
def _is_descriptor(obj):
"""Returns True if obj is a descriptor, False otherwise."""
return (
hasattr(obj, '__get__') or
hasattr(obj, '__set__') or
hasattr(obj, '__delete__'))
def _is_dunder(name):
"""Returns True if a __dunder__ name, False otherwise."""
return (name[:2] == name[-2:] == '__' and
name[2:3] != '_' and
name[-3:-2] != '_' and
len(name) > 4)
def _is_sunder(name):
"""Returns True if a _sunder_ name, False otherwise."""
return (name[0] == name[-1] == '_' and
name[1:2] != '_' and
name[-2:-1] != '_' and
len(name) > 2)
def _make_class_unpicklable(cls):
"""Make the given class un-picklable."""
def _break_on_call_reduce(self, proto):
raise TypeError('%r cannot be pickled' % self)
cls.__reduce_ex__ = _break_on_call_reduce
cls.__module__ = '<unknown>'
class _EnumDict(dict):
"""Track enum member order and ensure member names are not reused.
EnumMeta will use the names found in self._member_names as the
enumeration member names.
def __init__(self):
self._member_names = []
def __setitem__(self, key, value):
"""Changes anything not dundered or not a descriptor.
If an enum member name is used twice, an error is raised; duplicate
values are not checked for.
Single underscore (sunder) names are reserved.
if _is_sunder(key):
raise ValueError('_names_ are reserved for future Enum use')
elif _is_dunder(key):
elif key in self._member_names:
# descriptor overwriting an enum?
raise TypeError('Attempted to reuse key: %r' % key)
elif not _is_descriptor(value):
if key in self:
# enum overwriting a descriptor?
raise TypeError('Key already defined as: %r' % self[key])
super().__setitem__(key, value)
# Dummy value for Enum as EnumMeta explicitly checks for it, but of course
# until EnumMeta finishes running the first time the Enum class doesn't exist.
# This is also why there are checks in EnumMeta like `if Enum is not None`
Enum = None
class EnumMeta(type):
"""Metaclass for Enum"""
def __prepare__(metacls, cls, bases):
return _EnumDict()
def __new__(metacls, cls, bases, classdict):
# an Enum class is final once enumeration items have been defined; it
# cannot be mixed with other types (int, float, etc.) if it has an
# inherited __new__ unless a new __new__ is defined (or the resulting
# class will fail).
member_type, first_enum = metacls._get_mixins_(bases)
__new__, save_new, use_args = metacls._find_new_(classdict, member_type,
# save enum items into separate mapping so they don't get baked into
# the new class
members = {k: classdict[k] for k in classdict._member_names}
for name in classdict._member_names:
del classdict[name]
# check for illegal enum names (any others?)
invalid_names = set(members) & {'mro', }
if invalid_names:
raise ValueError('Invalid enum member name: {0}'.format(
# create a default docstring if one has not been provided
if '__doc__' not in classdict:
classdict['__doc__'] = 'An enumeration.'
# create our new Enum type
enum_class = super().__new__(metacls, cls, bases, classdict)
enum_class._member_names_ = [] # names in definition order
enum_class._member_map_ = OrderedDict() # name->value map
enum_class._member_type_ = member_type
# save attributes from super classes so we know if we can take
# the shortcut of storing members in the class dict
base_attributes = {a for b in bases for a in b.__dict__}
# Reverse value->name map for hashable values.
enum_class._value2member_map_ = {}
# If a custom type is mixed into the Enum, and it does not know how
# to pickle itself, pickle.dumps will succeed but pickle.loads will
# fail. Rather than have the error show up later and possibly far
# from the source, sabotage the pickle protocol for this class so
# that pickle.dumps also fails.
# However, if the new class implements its own __reduce_ex__, do not
# sabotage -- it's on them to make sure it works correctly. We use
# __reduce_ex__ instead of any of the others as it is preferred by
# pickle over __reduce__, and it handles all pickle protocols.
if '__reduce_ex__' not in classdict:
if member_type is not object:
methods = ('__getnewargs_ex__', '__getnewargs__',
'__reduce_ex__', '__reduce__')
if not any(m in member_type.__dict__ for m in methods):
# instantiate them, checking for duplicates as we go
# we instantiate first instead of checking for duplicates first in case
# a custom __new__ is doing something funky with the values -- such as
# auto-numbering ;)
for member_name in classdict._member_names:
value = members[member_name]
if not isinstance(value, tuple):
args = (value, )
args = value
if member_type is tuple: # special case for tuple enums
args = (args, ) # wrap it one more time
if not use_args:
enum_member = __new__(enum_class)
if not hasattr(enum_member, '_value_'):
enum_member._value_ = value
enum_member = __new__(enum_class, *args)
if not hasattr(enum_member, '_value_'):
enum_member._value_ = member_type(*args)
value = enum_member._value_
enum_member._name_ = member_name
enum_member.__objclass__ = enum_class
# If another member with the same value was already defined, the
# new member becomes an alias to the existing one.
for name, canonical_member in enum_class._member_map_.items():
if canonical_member._value_ == enum_member._value_:
enum_member = canonical_member
# Aliases don't appear in member names (only in __members__).
# performance boost for any member that would not shadow
# a DynamicClassAttribute
if member_name not in base_attributes:
setattr(enum_class, member_name, enum_member)
# now add to _member_map_
enum_class._member_map_[member_name] = enum_member
# This may fail if value is not hashable. We can't add the value
# to the map, and by-value lookups for this value will be
# linear.
enum_class._value2member_map_[value] = enum_member
except TypeError:
# double check that repr and friends are not the mixin's or various
# things break (such as pickle)
for name in ('__repr__', '__str__', '__format__', '__reduce_ex__'):
class_method = getattr(enum_class, name)
obj_method = getattr(member_type, name, None)
enum_method = getattr(first_enum, name, None)
if obj_method is not None and obj_method is class_method:
setattr(enum_class, name, enum_method)
# replace any other __new__ with our own (as long as Enum is not None,
# anyway) -- again, this is to support pickle
if Enum is not None:
# if the user defined their own __new__, save it before it gets
# clobbered in case they subclass later
if save_new:
enum_class.__new_member__ = __new__
enum_class.__new__ = Enum.__new__
return enum_class
def __call__(cls, value, names=None, *, module=None, qualname=None, type=None, start=1):
"""Either returns an existing member, or creates a new enum class.
This method is used both when an enum class is given a value to match
to an enumeration member (i.e. Color(3)) and for the functional API
(i.e. Color = Enum('Color', names='red green blue')).
When used for the functional API:
`value` will be the name of the new class.
`names` should be either a string of white-space/comma delimited names
(values will start at `start`), or an iterator/mapping of name, value pairs.
`module` should be set to the module this class is being created in;
if it is not set, an attempt to find that module will be made, but if
it fails the class will not be picklable.
`qualname` should be set to the actual location this class can be found
at in its module; by default it is set to the global scope. If this is
not correct, unpickling will fail in some circumstances.
`type`, if set, will be mixed in as the first base class.
if names is None: # simple value lookup
return cls.__new__(cls, value)
# otherwise, functional API: we're creating a new Enum type
return cls._create_(value, names, module=module, qualname=qualname, type=type, start=start)
def __contains__(cls, member):
return isinstance(member, cls) and member._name_ in cls._member_map_
def __delattr__(cls, attr):
# nicer error message when someone tries to delete an attribute
# (see issue19025).
if attr in cls._member_map_:
raise AttributeError(
"%s: cannot delete Enum member." % cls.__name__)
def __dir__(self):
return (['__class__', '__doc__', '__members__', '__module__'] +
def __getattr__(cls, name):
"""Return the enum member matching `name`
We use __getattr__ instead of descriptors or inserting into the enum
class' __dict__ in order to support `name` and `value` being both
properties for enum members (which live in the class' __dict__) and
enum members themselves.
if _is_dunder(name):
raise AttributeError(name)
return cls._member_map_[name]
except KeyError:
raise AttributeError(name) from None
def __getitem__(cls, name):
return cls._member_map_[name]
def __iter__(cls):
return (cls._member_map_[name] for name in cls._member_names_)
def __len__(cls):
return len(cls._member_names_)
def __members__(cls):
"""Returns a mapping of member name->value.
This mapping lists all enum members, including aliases. Note that this
is a read-only view of the internal mapping.
return MappingProxyType(cls._member_map_)
def __repr__(cls):
return "<enum %r>" % cls.__name__
def __reversed__(cls):
return (cls._member_map_[name] for name in reversed(cls._member_names_))
def __setattr__(cls, name, value):
"""Block attempts to reassign Enum members.
A simple assignment to the class namespace only changes one of the
several possible ways to get an Enum member from the Enum class,
resulting in an inconsistent Enumeration.
member_map = cls.__dict__.get('_member_map_', {})
if name in member_map:
raise AttributeError('Cannot reassign members.')
super().__setattr__(name, value)
def _create_(cls, class_name, names=None, *, module=None, qualname=None, type=None, start=1):
"""Convenience method to create a new Enum class.
`names` can be:
* A string containing member names, separated either with spaces or
commas. Values are incremented by 1 from `start`.
* An iterable of member names. Values are incremented by 1 from `start`.
* An iterable of (member name, value) pairs.
* A mapping of member name -> value pairs.
metacls = cls.__class__
bases = (cls, ) if type is None else (type, cls)
classdict = metacls.__prepare__(class_name, bases)
# special processing needed for names?
if isinstance(names, str):
names = names.replace(',', ' ').split()
if isinstance(names, (tuple, list)) and isinstance(names[0], str):
names = [(e, i) for (i, e) in enumerate(names, start)]
# Here, names is either an iterable of (name, value) or a mapping.
for item in names:
if isinstance(item, str):
member_name, member_value = item, names[item]
member_name, member_value = item
classdict[member_name] = member_value
enum_class = metacls.__new__(metacls, class_name, bases, classdict)
# TODO: replace the frame hack if a blessed way to know the calling
# module is ever developed
if module is None:
module = sys._getframe(2).f_globals['__name__']
except (AttributeError, ValueError) as exc:
if module is None:
enum_class.__module__ = module
if qualname is not None:
enum_class.__qualname__ = qualname
return enum_class
def _get_mixins_(bases):
"""Returns the type for creating enum members, and the first inherited
enum class.
bases: the tuple of bases that was given to __new__
if not bases:
return object, Enum
# double check that we are not subclassing a class with existing
# enumeration members; while we're at it, see if any other data
# type has been mixed in so we can use the correct __new__
member_type = first_enum = None
for base in bases:
if (base is not Enum and
issubclass(base, Enum) and
raise TypeError("Cannot extend enumerations")
# base is now the last base in bases
if not issubclass(base, Enum):
raise TypeError("new enumerations must be created as "
"`ClassName([mixin_type,] enum_type)`")
# get correct mix-in type (either mix-in type of Enum subclass, or
# first base if last base is Enum)
if not issubclass(bases[0], Enum):
member_type = bases[0] # first data type
first_enum = bases[-1] # enum type
for base in bases[0].__mro__:
# most common: (IntEnum, int, Enum, object)
# possible: (<Enum 'AutoIntEnum'>, <Enum 'IntEnum'>,
# <class 'int'>, <Enum 'Enum'>,
# <class 'object'>)
if issubclass(base, Enum):
if first_enum is None:
first_enum = base
if member_type is None:
member_type = base
return member_type, first_enum
def _find_new_(classdict, member_type, first_enum):
"""Returns the __new__ to be used for creating the enum members.
classdict: the class dictionary given to __new__
member_type: the data type whose __new__ will be used by default
first_enum: enumeration to check for an overriding __new__
# now find the correct __new__, checking to see of one was defined
# by the user; also check earlier enum classes in case a __new__ was
# saved as __new_member__
__new__ = classdict.get('__new__', None)
# should __new__ be saved as __new_member__ later?
save_new = __new__ is not None
if __new__ is None:
# check all possibles for __new_member__ before falling back to
# __new__
for method in ('__new_member__', '__new__'):
for possible in (member_type, first_enum):
target = getattr(possible, method, None)
if target not in {
__new__ = target
if __new__ is not None:
__new__ = object.__new__
# if a non-object.__new__ is used then whatever value/tuple was
# assigned to the enum member name will be passed to __new__ and to the
# new enum member's __init__
if __new__ is object.__new__:
use_args = False
use_args = True
return __new__, save_new, use_args
class Enum(metaclass=EnumMeta):
"""Generic enumeration.
Derive from this class to define new enumerations.
def __new__(cls, value):
# all enum instances are actually created during class construction
# without calling this method; this method is called by the metaclass'
# __call__ (i.e. Color(3) ), and by pickle
if type(value) is cls:
# For lookups like Color(
return value
# by-value search for a matching enum member
# see if it's in the reverse mapping (for hashable values)
if value in cls._value2member_map_:
return cls._value2member_map_[value]
except TypeError:
# not there, now do long search -- O(n) behavior
for member in cls._member_map_.values():
if member._value_ == value:
return member
raise ValueError("%r is not a valid %s" % (value, cls.__name__))
def __repr__(self):
return "<%s.%s: %r>" % (
self.__class__.__name__, self._name_, self._value_)
def __str__(self):
return "%s.%s" % (self.__class__.__name__, self._name_)
def __dir__(self):
added_behavior = [
for cls in self.__class__.mro()
for m in cls.__dict__
if m[0] != '_' and m not in self._member_map_
return (['__class__', '__doc__', '__module__'] + added_behavior)
def __format__(self, format_spec):
# mixed-in Enums should use the mixed-in type's __format__, otherwise
# we can get strange results with the Enum name showing up instead of
# the value
# pure Enum branch
if self._member_type_ is object:
cls = str
val = str(self)
# mix-in branch
cls = self._member_type_
val = self._value_
return cls.__format__(val, format_spec)
def __hash__(self):
return hash(self._name_)
def __reduce_ex__(self, proto):
return self.__class__, (self._value_, )
# DynamicClassAttribute is used to provide access to the `name` and
# `value` properties of enum members while keeping some measure of
# protection from modification, while still allowing for an enumeration
# to have members named `name` and `value`. This works because enumeration
# members are not set directly on the enum class -- __getattr__ is
# used to look them up.
def name(self):
"""The name of the Enum member."""
return self._name_
def value(self):
"""The value of the Enum member."""
return self._value_
def _convert(cls, name, module, filter, source=None):
Create a new Enum subclass that replaces a collection of global constants
# convert all constants from source (or module) that pass filter() to
# a new Enum called name, and export the enum and its members back to
# module;
# also, replace the __reduce_ex__ method so unpickling works in
# previous Python versions
module_globals = vars(sys.modules[module])
if source:
source = vars(source)
source = module_globals
members = {name: value for name, value in source.items()
if filter(name)}
cls = cls(name, members, module=module)
cls.__reduce_ex__ = _reduce_ex_by_name
module_globals[name] = cls
return cls
class IntEnum(int, Enum):
"""Enum where members are also (and must be) ints"""
def _reduce_ex_by_name(self, proto):
def unique(enumeration):
"""Class decorator for enumerations ensuring unique member values."""
duplicates = []
for name, member in enumeration.__members__.items():
if name !=
if duplicates:
alias_details = ', '.join(
["%s -> %s" % (alias, name) for (alias, name) in duplicates])
raise ValueError('duplicate values found in %r: %s' %
(enumeration, alias_details))
return enumeration